Process and apparatus for metal refining

ABSTRACT

The invention is directed to a process and apparatus for metal refining, in particular for refining a mixture of conductive particles, such as heavy non-ferrous particles. In accordance with the invention a feed containing a mixture of conductive particles is fed to a dissolution unit, wherein the less noble metal is separated from a metal of interest in the presence of one or more acids or complexing agents, thus producing a stream having a concentrated less noble metal and producing a conductive stream containing a metal of interest. The conductive stream is then fed to a refining unit, wherein the conductive stream is separated in a stream of concentrated metal(s) of interest and a stream of concentrated conductive particles.

The invention is directed to a process and apparatus for metal refining,in particular for refining a mixture of conductive particles, such asmixtures of metallic particles. More particularly, the invention relatesto a process and apparatus to separate concentrated metal streams, suchas copper cathodes, zinc solutions or noble metal concentrates, frommixtures of heavy non-ferrous particles, containing for example copper,zinc, lead, and noble metals, with the particle sizes less than e.g. 40mm or less than e.g. 15 mm or less than e.g. 5 mm, preferably withparticles sizes smaller than 1 μm or smaller than 100 μm excluded.

Mixtures containing heavy non-ferrous particles are generally producedby shredding or incinerating waste (including waste to energyincineration) and secondary streams, such as municipal refuge andscrapped cars. From the generated mixture magnetic particles and lowdensity materials are removed. The ferromagnetic particles are commonlyremoved with magnetic belt separators, while the low density materialssuch as plastics are often removed by some combination of eddy currentseparators and density separators. Lighter non-ferrous metals can beremoved with heavy medium separators (as for instance disclosed inEP2412452), magnetic fluid separators or a variety of other well-knownprocesses such as gravity separation, sensor sorting. In this way, amixture of heavy non-ferrous particles is produced. Its compositiondepends strongly on the feed of the shredding or incineration process.

In the art, the mixture of heavy non-ferrous particles is usually soldto pyrometallurgical metal refiners. These refiners separate and upgradethe mixture by different processes which can contain melting, addingvirgin metals, oxidizing at elevated temperatures and casting anodes,which are only then electrolytically refined. The value of the mixtureof heavy non-ferrous particles is this way therefore generally lowerthan the sum of the value of the pure metals in the mixture. Also thepyrometallurgical processes have a high energy consumption and requirelarge feed streams to be economical, which results in distanttransporting of the mixture to central locations. The present inventiondoes not require casting of anodes, adding virgin etcetera.

Some existing hydrometallurgical methods, as for instance disclosed inU.S. Pat. No. 7,799,184 purify valuable metals from mixtures ofconductive particles by electrochemical decomposition of powders.However, this method is not versatile since less noble metals are notseparated from the mixture of conductive particles. The presence of lessnoble metals hampers the purification of the desired metal by build-upof less noble metals in the electrolyte.

In alternative hydrometallurgical methods as e.g. disclosed in WO2011/074948, WO 98/58090, US 2009/0074639, US 2006/0011014, and US2009/0183997, valuable metals of interest are purified from mixturesusing a combination of leaching and electrowinning. The metal ofinterest is first dissolved in a leaching step and subsequentlyrecovered from solution by a electrowinning step. It would be desirableto make these processes more energy efficient and find a solution to theliquid waste stream created in these processes.

The present invention seeks to provide a process and an apparatus topurify metals, including but not limited to copper, zinc, lead, gold andsilver from mixtures of conductive particles in order to give them morevalue and to reduce energy consumption compared to currently knownprocesses. Also the invention aims to be more suitable for a smallerfeed stream, thereby preventing distant transport of the mixture.Furthermore, production of environment-polluting residues is minimized.

It was found that these objects can be met by a process for recovering ametal of interest from a mixture of conductive particles comprising saidmetal of interest, which process comprises:

a) feeding said mixture of conductive particles to a separation unit,wherein a less noble metal is separated from the metal of interest byselective leaching, thus producing a concentrated stream comprising theless noble metal and a conductive stream comprising the metal ofinterest;

b) followed by a step of separating the metal of interest from saidconductive stream by electro-refining, thus producing a streamcomprising the metal of interest and a stream of concentrated conductivematerials.

In the second step (b) of the present invention, the metal of interestcan be plated onto cathodes using an electrical current whereby saidconductive stream comprising the metal of interest is used as anode. Togreat advantage, this anode might be placed vertically using for exampletwo perforated plates to hold the conductive stream, through which theelectrolyte is pumped. A vertically placed anode allows for a goodelectrical field in combination with a vertical cathode, therebyproducing high quality plated metal with little impurities. Preferably,the recovered metal of interest on the cathode has a purity of more than95 wt. %, more preferably more than 98 wt. %, most preferably more than99.5 wt. %.

FIG. 1 is a schematic representation of a particular embodiment of thepresent invention.

FIG. 2 is a schematic representation of an embodiment of an apparatus inaccordance with the present invention.

In the present invention, first the less noble metals is separated fromthe mixture (step a), thereby making the process more versatile. As aresult, the process may also be used to treat mixtures comprising theseless noble metals.

Advantageously, the present invention enables concentration of metalspreferably by plating them onto cathodes, separate as fine particles orseparate as large particles, such that the separation of metals is morefacile and the energy intensive leaching/recovery cycle is not necessaryfor the metals of interest.

The present invention does not use a two-step process for the separationof metals of interest, i.e. leaching the metal of interest followed byelectrowinning. Instead, a concentrated metal stream, comprising themetals of interest, is produced directly from a conductive stream and inthe same unit, preferably by electro-refining, thereby decreasing energyconsumption. The leaching in the present invention involves the lessnoble metal is are not electrolytically recovered (i.e. selectiveleaching).

In the present invention, the degree of nobility of metals is related tothe metal of interest in accordance with the galvanic series in theenvironment. For example, if the metal of interest is copper, zinc wouldbe a less noble metal and gold would be a more noble metal.

For purpose of clarity and concise description, the metal of interestmay be one or more metals of interest. Likewise, the less noble metalmay be one or more less noble metals. The more noble metal may be morethan one more noble metal.

In a preferred embodiment, the process of the present inventioncomprises an additional step c) wherein a more noble metal is separatedas fine particles from said concentrated conductive stream, thusproducing said stream of more noble metals and a stream of concentratedconductive particles.

In a particular embodiment of the present invention, said metal ofinterest comprises copper.

In another particular embodiment of the present invention, said lessnoble metal comprises zinc.

In yet another particular embodiment of the present invention, said morenoble metal comprises gold.

In another preferred embodiment, in an additional step of the presentinvention, the spent acids or complexing agents are treated with thestream of concentrated conductive particles, so that the acids orcomplexing agents can be re-used.

The metal of interest is present in a mixture of conductive particles,which is used as a feed for the present invention. Typically, themixture of conductive particles is a concentrate that originates fromash (e.g. bottom ash) from an incineration process (including waste toenergy incineration) or from a shredding process of e.g. scrapped cars.Preferably, the mixture of conductive particles is a non-ferrous mixtureof conductive particles since ferrous particles are typically removedfrom waste before or after the incineration of the waste.

The mixture of conductive particles is thus generally a secondary (ornon-primary) source of the metal of interest. Metal ore that isextracted in the traditional mining industry is herein considered as theprimary source for the metal of interest. It may be appreciated that themixture of conductive particles originating from secondary sourcesdiffers significantly from ore mixtures from the mining industry.

The mixture of conductive particles in accordance with the presentinvention commonly comprises a large number of different metals, e.g. upto about 18 different metals. Typically, the mixture of conductiveparticles comprises three or more metals, such as between five to twentydifferent metals in amount of more than 0.1 ppm of the total atomiccomposition.

The mixture typically comprises 20 to 80 wt. %, preferably 30 to 60 wt.% copper (based on the total mass of the dry solids in the mixture ofconductive particles).

The mixture of conductive particles further typically comprises 5 to 40wt. %, preferably 10 to 30 wt. % zinc (based on the total mass of thedry solids in the mixture of conductive particles).

Typically waste streams from e.g. shredders or municipal waste treatmentfacilities also comprises small amounts of noble metals such as silverand gold. Consequently, the mixture of conductive particles inaccordance with the present invention generally comprises gold in anamount of 1 to 300 ppm, preferably in an amount of 10 to 100 ppm (basedon the total mass of the dry solids in the mixture of conductiveparticles). The mixture typically further comprises silver in an amountof 50 to 4000 ppm, preferably in an amount of 1000 to 2500 ppm (based onthe total mass of the dry solids in the mixture of conductiveparticles).

Typically, the mixture of conductive particles comprises at least three,preferably more than ten, most preferably more than twelve differentmetals, which are preferably selected from the group consisting ofsilver, gold, platinum, palladium, lead, copper, nickel, zinc, tin,alumina, iron, cadmium, beryllium, chromium, cobalt, manganese, antimonyand vanadium.

It may be appreciated that the mixture of conductive particle may alsocomprise non-conductive and/or non-metallic particles such as silicatesoriginating e.g. from glass waste as long as the conductive propertiesof the mixture as a whole are not rendered null.

The metal of interest may be present in their metallic or oxidized form,as long as it is still conductive and may be (further) oxidized. Thepresent inventors realized that typically the metals of interest, inparticular copper, are frequently present in metallic form and that inorder to select the metals and to concentrate them, it is very importantto select the right acid or complexing agents or the right combinationof acids or complexing agents, both with the right pH.

Furthermore, it is highly advantageous to select the right voltage forthe electrochemical recovery.

In the first step (a) of the present invention, the less noble metal ispreferably separated from a conductive supply stream (herein alsoreferred to as the mixture of conductive particles) in the presence of alixiviant. The lixiviant typically contains one of more acids orcomplexing agents, e.g. sulfuric acid, hydrochloric acid, nitric acid,ammonia, cyanide, hydroxide or the like. Said less noble metal ischemically converted into a salt that is dissolved in aqueous media,such as water. This process may be referred to as selective leaching.The metal of interest that is to be recovered is not converted into anin aqueous media soluble salt. Step a) thus involves selective leachingof the less noble metal to separate this from at least one metal ofinterest. This results in high less noble metal concentrations. Forexample in zinc concentrations of 20-200 g/L in a sulfate solution witha pH range of 0-1. Preferably this step is operated at elevatedtemperatures, more specifically at temperatures around 50° C. Typicallythe following reaction occurs, wherein zinc is used as an example:

Zn(s)+2H⁺(aq)→H₂(g)+Zn²⁺(aq)   (1)

After the less noble metal is converted into in aqueous media solublemetal salts and removed as a liquid stream, preferably to a considerableextent, e.g. 75% (based on weight) or more, the metals of interest isseparated from said conductive stream (step b of the present invention),preferably to a considerable extent, e.g. 70% to 90% (based on weight).This is preferably done with an electro-refining step. The conditions inthe electro-refining step need to be chosen such that a selection andpurification of the metal of interest is achieved.

Electro-refining is a method to purify a mix of different metals. Thisstep is typically carried out using an electrolytic cell, preferablywherein one or more pairs of negative cathodes and positive anodes arepresent. More preferably, the number of anodes is one more than thenumber of cathodes, such that the metal of interest may be plated onboth sides of each cathode (FIG. 2). Said conductive stream (i.e. thestream obtained after the separation of the less noble metal), may beused as anode. At the anode, one or more metals of interest willdissolve as ions in the electrolyte. Typically, the electrolytecomprises sulfuric acid, hydrochloric acid, nitric acid ammonia,cyanide, hydroxide or a combination thereof. The dissolved ions of themetal of interest are then reduced on the cathode in the same unit, thusforming a metal deposit on the cathode. The metal deposit on the cathodecan later be easily removed. The electro-refining process is preferablydriven by a direct current or by a reverse pulse modulated current. Forcopper, the voltage is preferably between 0.01 V and 1 V, morepreferably between 0.3 and 0.5 V.

The used electrolyte is preferably 20-30 wt % sulfuric acid with aconcentration of ions of the metal of interest (e.g. Cu²⁺ and/or ions ofother metals of interest) between 20 and 45 g/L and/or with a pH rangeof −0.5 and 0.5. Electro-refining is preferably performed at elevatedtemperatures, more preferably at temperatures around 50° C.

By illustration, the following two half-reactions may take place,wherein copper is used as an example:

at the anode: Cu(s)→Cu²⁺+2e⁻,

and at the cathode: Cu²⁺+2e⁻→Cu(s).

The concentration of ions of the metal of interest in the electrolyteneeds to be kept constant or substantially constant. However, these ionsare expended as long as there are less noble metals present in the anoderesulting in spent electrolyte. For instance zinc versus copper, theleaching of zinc follows the reaction: Zn(s)+Cu²⁺→Zn²⁺+Cu(s), whichdepletes the electrolyte.

By illustration, the following two half-reactions may take place forzinc and copper:

at the anode: Zn(s)→Zn²⁺+2e⁻,

and at the cathode: Cu²⁺+2e⁻→Cu(s).

For this reason the spent electrolyte is additionally reprocessed in astep of the process of the present invention . In this step the metal ofinterest is dissolved in the spent electrolyte, in order to compensatefor the depletion of ions from the electrolyte (this step may also bereferred to as regeneration of the electrolyte). This is preferably doneby adding an electron acceptor, e.g. an oxygen containing gas, such asair, to a bed of particles containing a dissolvable metal of interest.

After the electro-refining step b), the stream of concentratedconductive materials typically still comprise part of the metal ofinterest (i.e. the part that is not yet recovered in step b), alsoreferred to as notyet recovered metal of interest), typically in anamount of 10-30% of the amount of the metal of interest in the mixtureof conductive particles. Preferably, this not yet recovered metal ofinterest is used for the regeneration of the electrolyte. For example, apacked bed of particles containing dissolvable not yet recovered metalof interest and an electron acceptor are contacted with the spentelectrolyte in which the metal of interest dissolves. By illustration,the following two half-reactions may take place by addition of electronacceptor in order to compensate for the depletion of the electrolyte.For example by using an oxygen containing gas as electron acceptor andcopper as the metal of interest:

anodic: Cu(s)→Cu²⁺+2e⁻,

cathodic: O₂+2H⁺+4e⁻→2OH⁻.

Since the reaction takes place under acidic conditions, it may beappreciated that the two-half reactions may also be represented by:

anodic: Cu(s)→Cu²⁺+2e⁻,

cathodic: O₂+4H⁺+4e⁻→2H₂O

To great advantage the dissolution of the metal of interest in the spentelectrolyte and thus the regeneration of the electrolyte is acceleratedby using ammonia as catalyst. To great advantage this dissolution isaccelerated by elevating the temperature to at least 50° C.

In the concentrated conductive stream, typically high value metalsremain present that are more noble than the metal of interest. Theconcentrated conductive stream that is obtainable by the presentinvention is very characteristic in its chemical composition, inparticular in case the mixture of conductive particles originates fromsecondary sources (vide supra).

The process in accordance with the present invention typically resultsin a concentrated conductive stream that comprises silver and/or gold.In a preferred embodiment, the concentrated conductive stream comprisesat least three, preferably more than ten, most preferably more thantwelve different metals, preferably selected from the group consistingof silver, gold, platinum, palladium, lead, nickel, tin, alumina, iron,cadmium, beryllium, chromium, cobalt, manganese, antimony and vanadium.More preferably, the concentrated conductive stream comprises at leastgold and/or silver.

The concentrated conductive stream preferably comprises less than 20 wt.%, more preferably less than 10 wt. % copper and/or less than 10 wt. %,more preferably less than 5 wt. % zinc (based on the total mass of thedry solids in concentrated conductive stream).

Preferably, the concentrated conductive stream comprises gold in anamount of more than 150 ppm, preferably more than 500 ppm. Typically,the concentrated conductive stream comprises gold in an amount of up to5000 ppm, more preferably in an amount of up to 10000 ppm (based on thetotal mass of the dry solids in the concentrated conductive stream).

Preferably, the concentrated conductive stream comprises silver in anamount of more than 4000, preferably more than 10000 ppm. Typically, theconcentrated conductive stream comprises silver in an amount of up to25000 ppm, more preferably in an amount of up to 100000 ppm (based onthe total mass of the dry solids in the concentrated conductive stream).

Exact concentrations and even the presence of the metals may vary basedon the chemical composition of the feed stock (i.e. mixture ofconductive particles). Metals that are typically present in theconcentrated conductive stream are provided in table 1 (concentrationsbased on the total mass of the dry solids in the concentrated conductivestream). For sake of conciseness and clarity, all metals are given in asingle overview. However, it may be appreciated that, for the reasonsprovided above, the composition of the concentrated conductive streammay be any combination of any of the given metals in any of the givenconcentrations.

The concentration of in particular nickel, iron, tin, aluminum, cadmium,beryllium, cobalt, manganese, antimony and/or vanadium are generallylower than the concentration of other metals and may vary significantlyon the type and composition of the source material used for the presentinvention. Concentrations are therefore indicated as either small ortrace (i.e. less than small) amounts.

TABLE 1 range Metal Concentration about min max Ag [ppm] 6330 2500 15000Au [ppm] 250 40 800 Pt [ppm] 7 0.2 30 Pd [ppm] 42 1 160 Pb [%] 16 21.550 Cu [%] 17 8 30 Cr [ppm] 1568 200 10000 Zn [%] 7 2.0 15 Ni Smallamounts Fe Small amounts Sn Trace amounts Al Trace amounts Cd Traceamounts Be Trace amounts Co Trace amounts Mn Trace amounts Sb Traceamounts V Trace amounts

From the concentrated conductive stream, which remains after theelectro-refining step, additionally a more noble metal may be separated(i.e. step c) by for example filtration. The present inventors realizedthat such a more noble metal of interest, e.g. gold or silver, isusually present as a coating of the conductive particles. When theconductive particles are partially dissolved in prior leaching and/orelectro-refining steps, small particles of this more noble metal willremain. These small particles are then concentrated by using a filter.This is preferably done during the electro-refining step, by circulatingthe electrolyte through the electrolytic cell. The electrolyte willtransport the small particles out of the electrolytic cell. Aconcentrated noble metal stream can be obtained by filtering theelectrolyte. For instance, gold may typically be obtained in aconcentration of 2000 to 8000 ppm (based on the total mass of theconcentrated noble metal stream).

In a preferred embodiment of the present invention, part of the spentelectrolyte from step b) is used in step a) as lixiviant. This waybuildup of ions of the less noble metal(s), e.g. zinc, in theelectrolyte is prevented. In this case the reaction in step b) initiallychanges, whereby ions of the metal of interest are cemented onto theparticles, and are thus not lost as aqueous media soluble salt, becausethey can be extracted again in step b) or d). Typically the followingreaction occurs, wherein copper and zinc are used as an example:

Zn(s)+Cu²⁺(aq)→Cu(s)+Zn²⁺(aq)   (2)

Additionally, the inventors realized that in the remaining concentratedconductive stream, high concentrations of metals, such as noble metalsand lead, are present that are not removed during the steps a) and b) ofthe present process. This remaining solid stream is more concentrated inthese metals after steps a and b of the present process, thereby makingthe mixture more suitable for further refining. This refining iscommonly done by pyrometallurgical processes. However, some initialrefining can be achieved by a novel step. Accordingly, in a preferredembodiment of the present invention steps a) and b) are followed by afurther refining step, thereby separating at least one more noble metalof interest from said concentrated conductive stream, thus producing astream of concentrated more noble metals and a second stream ofconcentrated conductive materials. It may be appreciated that in casesaid step of further refining is applied, step c) may be performed onthe second stream of concentrated conductive materials.

In FIG. 1 a schematic representation of a particular embodiment of thepresent invention is depicted. A mixture of conductive particles (5)that is produced by for example an incinerator or shredder is fed to theseparation unit (1), wherein a less noble metal (7), e.g. zinc, isseparated from other metals in a dissolved form by feeding the lixiviant(9) wherein the less noble metal will dissolve (selective leaching). Thelixiviant (9) originates from the treatment of the spent electrolyte inthe regeneration process (4), this is preferred but not required. Theremaining solids (8) (resulting from the selective leaching in unit 1and also referred to herein as the conductive stream) are fed to anelectro-refining unit (2), where a metal of interest, e.g. copper, isseparated (10). The (regenerated) electrolyte (9) originates from thetreatment of the spent electrolyte (4), this is preferred but notrequired.

In a typical example of the electro-refining unit (FIG. 2), the anodes,comprising or consisting of solids (19) (also referred herein to theconductive stream), and a cathode plate, comprising a suitable metal,e.g. stainless steel or copper, (18) are used as electrodes. The anodekeeps its shape because it is supported by two perforated plates (20) ofa suitable material, e.g. stainless steel or PVC. Plates 20 form acompartment comprising the conductive stream (i.e. the anode) that isspaced from the cathode.

In a particular embodiment, multiple anodes and cathodes are used in analternating setup. Preferably the solids which remain after theelectrolytic treatment in electro-refining unit 2 (also referred toherein as the stream of concentrated conductive material), are used inthe electrolyte treatment step (16). The spent electrolyte (11) is fedto a filtration unit (3), where a more noble metal of interest, e.g.gold, is filtrated as particles from the spent electrolyte (11). Thenthe filtrated spent electrolyte (13) is fed to an electrolyte treatmentunit (4). An example of a method to treat the spent electrolyte is toblow an oxygen-containing gas, e.g. air, (14) through the spentelectrolyte (13) while it is in contact with particles that containdissolvable metal(s) of interest (i.e. not yet recovered metal ofinterest), e.g. particles in the stream of concentrated conductivematerials which remain after the electro-refining step (16). New (fresh)acid is added in this unit (15) in order to compensate for the acidwhich leaves the system with the pregnant lixiviant (7). If theremaining particles resulting from the electro-refining unit (16)(stream of concentrated conductive materials comprising non-recoveredmetal of interest) are used as the source for the ions to regeneratedthe electrolyte in the electrolyte treatment unit (4), then theremaining solids resulting from this unit (4) contain a highconcentration of other conductive particles, i.e. the more noble metale.g. lead and silver (17).

In a further aspect of the present invention, the inventor found that aparticular apparatus may be used that is suitable for carrying out thepresent invention.

The apparatus comprises a dissolution unit, which comprises an openingfor feeding a conductive supply stream, in particular a heavynon-ferrous mixture of particles produced by shredding or incineratingwaste and secondary streams; a refining unit, which comprises a duct forreceiving the effluent of said dissolution unit; the apparatuspreferably further comprises an electrolyte filtration unit, whichcomprises a duct for receiving the effluent of said refining unit.

Preferably, the apparatus further comprises an electrolyte treatmentunit that comprises a duct for receiving the spent electrolyte.Typically said refining unit is an electro-refining unit which comprisesperforated plates (typically based on non-conductive materials such asPVC or coated stainless steel) that form a compartment comprising theconductive stream as anode. Adjacent the compartment—and in case ofmultiple compartments, in between two compartments—a cathode is present.The electro-refining unit preferably comprises one or more verticalanodes and one or more cathodes preferably spaced in such a way that theconductive stream can be prevented from entering the space between eachcompartment when feeding with a tool and a short circuit is prevented.

In a preferred embodiment, the units are the size of a pallet box, forexample, the floor dimensions are near to those of an EURO pallet or anGMA pallet, with a height between 600 and 1200 mm. Also the flooring ofthe unit is such that it can be lifted and rotated upside down by aforklift, or other jacking device. This way the remaining solids can beeasily unloaded from the unit.

In a preferred embodiment, the perforated plates which support theanodes are spaced in such a way, that, when the unit is filled from thetop, a sieve or lattice can be used to guide the mixture of conductiveparticles between the perforated plates at the anode side and notbetween the perforated plates at the cathode side.

For the purpose of clarity and a concise description features aredescribed herein as part of the same or separate embodiments, however,it will be appreciated that the scope of the invention may includeembodiments having combinations of all or some of the featuresdescribed.

1. A process for recovering a metal of interest from a mixture ofconductive particles containing said metal of interest, as well as aless noble metal, which process comprises: a) feeding said mixture ofconductive particles to a separation unit, wherein the less noble metalis separated by selective leaching, thus producing a concentrated streamcomprising the less noble metal and producing a conductive streamcomprising the metal of interest; b) followed by a step of separatingthe metal of interest from said conductive stream by electro-refining,thus producing a stream comprising the metal of interest and a stream ofconcentrated conductive materials.
 2. The process according to claim 1,which is followed by a step c) of separating at least one more noblemetal from said concentrated conductive stream, thus producing a streamof concentrated more noble metals and a second stream of concentratedconductive materials.
 3. The process according to claim 1, wherein saidstep of separating the metal of interest from said conductive stream byelectro-refining is performed in an electrochemical cell, comprising ananode and a cathode, in the presence of an electrolyte comprising one ormore acids or complexing agents, wherein said conductive stream is theanode and the metal of interest is plated on the cathode.
 4. The processaccording to claim 3, wherein the electrolyte is spent and at least partof the spent electrolyte is used in the separation of the less noblemetal.
 5. The process according to claim 3, followed by a step oftreating at least part of the spent electrolyte and reusing theresulting treated electrolyte in the electrochemical cell.
 6. Theprocess according to claim 2, wherein said step of separating the morenoble metal comprises a filtration.
 7. The process according to claim 1,wherein said step of separating the less noble metal comprisesdissolving and oxidizing the less noble metals by the use of one or moreacids or complexing agents.
 8. The process according to claim 5, whereinsaid step of treating at least part of the spent electrolyte comprisesdissolution and oxidation of the (not yet recovered) metals of interestby the use of an electron acceptor, wherein said electron acceptor ispreferably an oxygen containing gas, more preferably air.
 9. The processaccording to claim 1, wherein said one or more acids or complexingagents comprised in the electrolyte are selected from the groupconsisting of H₂SO₄, HCl, HNO₃, NH₃, CN³¹ , OH⁻ and combinationsthereof.
 10. The process according to claim 1, wherein said mixture ofconductive particles containing said the metal of interest comprises aheavy non-ferrous mixture of particles originating from shredding orincinerating waste and secondary streams.
 11. The process according toclaim 2, wherein said metal of interest comprises copper, said lessnoble metal comprises zinc and/or said more noble metal comprises gold.12. Concentrated conductive materials obtainable by a process forrecovering a metal of interest from a mixture of conductive particlesaccording to claim 1, wherein the mixture of conductive particles is asecondary source of the metal of interest and said concentratedconductive materials comprise particles consisting of a more noble metalof interest such as gold or silver.
 13. The concentrated conductivematerials according to claim 12 comprising gold in an amount of at least150 ppm and/or silver in an amount of at least 4000 ppm (both based onthe total mass of the dry solids in the mixture of conductiveparticles); and further comprising at least three, selected from thegroup consisting of platinum, palladium, lead, copper, nickel, zinc,tin, alumina, iron, cadmium, beryllium, chromium, cobalt, manganese,antimony and vanadium.
 14. An apparatus for carrying out a processaccording to claim 1, comprising: a dissolution unit, which comprises anopening for feeding a conductive supply stream, in particular a heavynon-ferrous mixture of particles produced by shredding or incineratingwaste and secondary streams; a refining unit, which comprises a duct forreceiving the effluent of said dissolution unit; and optionally furthercomprising an electrolyte filtration unit, which comprises a duct forreceiving the effluent of said refining unit.
 15. The apparatusaccording to claim 14, further comprising an electrolyte treatment unithaving a duct for receiving the spent electrolyte.
 16. The apparatusaccording to claim 14, wherein said refining unit is an electro-refiningunit which comprises multiple perforated plates forming one or morecompartments which contain the conductive stream as anode, whereinadjacent to one or more compartment a cathode is present, optionallyspaced in such a way that the conductive stream can be prevented fromentering the space between the compartment and the cathode when feedingwith a tool.
 17. The apparatus according to claim 14, which comprises ofone or more units dimensioned the size of a pallet box, fitted withopenings such that it can be lifted and rotated upside down by aforklift, or other jacking device.